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Re: OT New Digital Mode and K3S Frequency Accuracy
 
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From the WSJT-X site:https://physics.princeton.edu/pulsar/k1jt/wsjtx.html
73 Bob, K4TAX NEW FEATURES IN WSJT-X Version 1.8.0 ------------------------------------ 1. New mode called FT8: sensitivity down to -20 dB on the AWGN channel; QSOs 4 times faster than JT65 or JT9; auto-sequencing includes an option to respond automatically to first decoded reply to your CQ. 2. New mode for accurate Frequency Calibration of your radio. 3. Improved performance of decoders for JT65, QRA64, and MSK144. MSK144 includes facilities for amplitude and phase equalization and an "SWL" mode for short-format messages. 4. Options to minimize screen space used by Main and Wide Graph windows. 5. Enhanced management scheme for table of operating frequencies, and a new set of default frequencies specific to the three IARU Regions. 6. Improved CAT control for many rigs, including those controlled through Commander or OmniRig. 7. New keyboard shortcuts to set "Tx even/1st" ON or OFF. 8. A number of (mostly minor) bug fixes and tweaks to the user interface. For example: new behavior for the audio level slider; correctly logged QSO start times in certain situations; correct control of FT-891/991 and some other radios via rigctld. At the time of the v1.8.0-rc1 release the following tasks are yet to be completed: 1. Updates to WSJT-X User Guide. 2. Sample files for FT8. 3. Enhanced FT8 decoding using AP ("a priori") information. 4. Signal subtraction and multi-pass decoding for FT8. 5. Option for FT8 to Auto-respond to the weakest responder to your CQ. Installation packages for Windows, Linux, OS X, and Raspbian can be downloaded from the WSJT web site: http://physics.princeton.edu/pulsar/K1JT/wsjtx.html Please send bug reports to either [hidden email] or [hidden email]. Such reports should include a full prescription of steps to reproduce the undesired behavior. You must be a subscriber to post to either of these lists. Brief Description of the FT8 Protocol ------------------------------------- WSJT-X Version 1.8.0 includes a new mode called FT8, developed by K9AN and K1JT. The mode name "FT8" stands for "Franke and Taylor, 8-FSK modulation". FT8 uses 15-second T/R sequences, provides 50% or better decoding probability down to -20 dB on an AWGN channel, and maintains good performance on Doppler-spread fading channels. An auto-sequencing facility includes an option to respond automatically to the first decoded reply to your CQ. FT8 QSOs are 4 times faster than those made with JT65 or JT9. FT8 is an excellent mode for HF DXing and for situations like multi-hop E_s on 6 meters, where deep QSB may make fast and reliable completion of QSOs desirable. Some important characteristics of FT8: - T/R sequence length: 15 s - Message length: 75 bits + 12-bit CRC - FEC code: LDPC(174,87) - Modulation: 8-FSK, tone spacing 6.25 Hz - Constant-envelope waveform - Occupied bandwidth: 50 Hz - Synchronization: 7x7 Costas arrays at start, middle, and end - Transmission duration: 79*1920/12000 = 12.64 s - Decoding threshold: -20 dB; several dB lower with AP decoding - Multi-decoder finds and decodes all FT8 signals in passband - Optional auto-sequencing and auto-reply to a CQ response - Operational behavior similar to JT9, JT65 We plan to implement signal subtraction, two-pass decoding, and use of a prior (AP) information in the decoder. These features are not yet activated in v1.8.0. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
Re: New Digital Mode and K3S Frequency Accuracy
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In reply to this post by Christopher Hoover
On 7/16/2017 10:54 AM, Christopher Hoover wrote:
> JT65 can decode arbitrary messages down to -24 dB (and certain messages > down to -32 dB). When functioning as a multi-decoder, late versions of WSJT-X often give me good decodes in the range of -24 to -29dB re: the full bandwidth noise floor, and they also include second-pass decoding for signals missed during the first pass. It is, for example, common to decode 2-3 responses to the same CQ, all within a few Hz of each other. Second pass decoding subtracts out the decoded signals and then decodes what's left. Particularly impressive was what happened when a W7-area station was calling JA7QVI on 6M, but got out of sync so that he was calling on the same cycle as JA7QVI. Both stations were decoded on consecutive passes, even though the W7-area station was 10-12 dB louder and nearly zero beat! JT65 often decodes signals that overlap each other. FT8 does not, but FT8 signals only occupy about one-quarter the bandwidth of a JT65 signal. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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I had limited time this weekend, and decided to operate only on 6 meters
using only the new FT8 digital mode. I operated for only one hour on Saturday evening and three hours on Sunday, mostly in the afternoon. My result was 70 QSOs in 35 grids. Of course it was much slower than CW and SSB but much faster than JT65 where the QSO rate would have been prohibitively slow. The number of QSOs could have been easily doubled with better propagation during the four hours when I was active. 22 QSOs were completed during which the FT8 software reported SNRs from my receiver below -10 dB. Some of these 22 QSOs may have been difficult to complete on CW. -11 dB 3 QSOs -12 dB 4 QSOs -13 dB 4 QSOs -15 dB 3 QSOs -16 dB 3 QSOs -17 dB 2 QSOs -18 dB 2 QSOs -19 dB 1 QSO There's an opportunity to significantly improve the FT8 contest QSO rate by introducing a Contest Mode that eliminates the 73 TX Message. In my opinion there's no need for the 73 TX Message in contests, if FT8 software doesn't receive the RRR message it automatically resends the previous TX message until the RRR message is received. If an RRR TX message is not received the QSO is not logged. This FT8 behavior is unambiguous with no need for the 73 TX Message. The 15 second sequences worked very well, there was never a need for additional delay between sequences because in almost every case when I started the next sequence a few seconds late the FT8 software decoded my transmission despite my delay. Better behavior of the automatic CQ reply function -- so that it functions exactly like double-clicking on the call of the station replying to a CQ -- would have eliminated most of those delayed TX messages It was a very enjoyable experience, kudos to the FT8 development team. 73 Frank W3LPL ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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